Semiquantitative Paper-Based Microfluidic Surrogate Virus Neutralization Test for SARS-CoV-2 Neutralizing Antibodies.

Neutralizing antibodies (nAbs) produced from infection or vaccination play an important role in acquired immunity. Determining virus-specific nAb titers is a useful tool for measuring aquired immunity in an individual. The standard methods to do so rely on titrating serum samples against live virus and monitoring viral infection in cultured cells which requires high biosafety level containment. The surrogate virus neutralization test (sVNT) reduces the biohazards and it is suitable for designing rapid test device in a lateral flow assay (LFA) format. Here, we introduce the fabrication and development of a unique paper-based LFA device for determining the level of SARS-CoV-2 nAb in a sample with a semiquantitative direct colorimetric readout. A LFA-based gradient assay design was used to facilitate the sVNT, where the spike glycoprotein receptor binding domain (RBD) and angiotensin-converting enzyme 2 (ACE2) stand in as proxies for viruses and cells, respectively. The gradient assay employed multiple test dots of ACE2 spotted in increasing concentration along the sample flow path and gold nanoparticle-conjugated RBD for readout. In this way, the number of developed spots is inversely proportional to the concentration of nAbs present in the sample. The assay was tested with both standard solutions of nAb as well as human serum samples. We have demonstrated that the device can effectively provide semiquantitative test results of nAbs by direct instrument-free colorimetric detection.

ATPSpin: A Single Microfluidic Platform that Produces Diversified ATPS-Alginate Microfibers.

Microfluidic spinning is emerging as a useful technique in the fabrication of alginate fibers, enabling applications in drug screening, disease modeling, and disease diagnostics. In this paper, by capitalizing on the benefits of aqueous two-phase systems (ATPS) to produce diverse alginate fiber forms, we introduce an ATPS-Spinning platform (ATPSpin). This ATPS-enabled method efficiently circumvents the rapid clogging challenges inherent to traditional fiber production techniques by regulating the interaction between alginate and cross-linking agents like Ba2+ ions. By varying system parameters under the guidance of a regime map, our system produces several fiber forms─solid, hollow, and droplet-filled─consistently and reproducibly from a single device. We demonstrate that the resulting alginate fibers possess distinct features, including biocompatibility. We also encapsulate HEK293 cells in the microfibers as a proof-of-concept that this versatile microfluidic fiber generation platform may have utility in tissue engineering and regenerative medicine applications.

Controlled Tempering of Lipid Concentration and Microbubble Shrinkage as a Possible Mechanism for Fine-Tuning Microbubble Size and Shell Properties.

The acoustic response of microbubbles (MBs) depends on their resonance frequency, which is dependent on the MB size and shell properties. Monodisperse MBs with tunable shell properties are thus desirable for optimizing and controlling the MB behavior in acoustics applications. By utilizing a novel microfluidic method that uses lipid concentration to control MB shrinkage, we generated monodisperse MBs of four different initial diameters at three lipid concentrations (5.6, 10.0, and 16.0 mg/mL) in the aqueous phase. Following shrinkage, we measured the MB resonance frequency and determined its shell stiffness and viscosity. The study demonstrates that we can generate monodisperse MBs of specific sizes and tunable shell properties by controlling the MB initial diameter and aqueous phase lipid concentration. Our results indicate that the resonance frequency increases by 180-210% with increasing lipid concentration (from 5.6 to 16.0 mg/mL), while the bubble diameter is kept constant. Additionally, we find that the resonance frequency decreases by 260-300% with an increasing MB final diameter (from 5 to 12 µm), while the lipid concentration is held constant. For example, our results depict that the resonance frequency increases by ∼195% with increasing lipid concentration from 5.6 to 16.0 mg/mL, for ∼11 µm final diameter MBs. Additionally, we find that the resonance frequency decreases by ∼275% with increasing MB final diameter from 5 to 12 µm when we use a lipid concentration of 5.6 mg/mL. We also determine that MB shell viscosity and stiffness increase with increasing lipid concentration and MB final diameter, and the level of change depends on the degree of shrinkage experienced by the MB. Specifically, we find that by increasing the concentration of lipids from 5.6 to 16.0 mg/mL, the shell stiffness and viscosity of ∼11 µm final diameter MBs increase by ∼400 and ∼200%, respectively. This study demonstrates the feasibility of fine-tuning the MB acoustic response to ultrasound by tailoring the MB initial diameter and lipid concentration.

Microfluidic nanobubbles: observations of a sudden contraction of microbubbles into nanobubbles.

Microfluidic devices are often utilized to generate uniform-size microbubbles. In most microfluidic bubble generation experiments, once the bubbles are formed the gas inside the bubbles begin to dissolve into the surrounding aqueous environment. The bubbles shrink until they attain an equilibrium size dictated by the concentration and type of amphiphilic molecules stabilizing the gas-liquid interface. Here, we exploit this shrinkage mechanism, and control the solution lipid concentration and microfluidic geometry, to make monodisperse bulk nanobubbles. Interestingly, we make the surprising observation of a critical microbubble diameter above and below which the scale of bubble shrinkage dramatically changes. Namely, microbubbles generated with an initial diameter larger than the critical diameter shrinks to a stable diameter that is consistent with previous literature. However, microbubbles that are initially smaller than the critical diameter experience a sudden contraction into nanobubbles whose size is at least an order-of-magnitude below expectations. We apply electron microscopy and resonance mass measurement methods to quantify the size and uniformity of the nanobubbles, and probe the dependence of the critical bubble diameter on the lipid concentration. We anticipate that further analysis of this unexpected microbubble sudden contraction regime can lead to more robust technologies for making monodisperse nanobubbles.

Microfluidically-generated Encapsulated Spheroids (µ-GELS): An All-Aqueous Droplet Microfluidics Platform for Multicellular Spheroids Generation.

Spheroids are three-dimensional clusters of cells that serve as in vitro tumor models to recapitulate in vivo morphology. A limitation of many existing on-chip platforms for spheroid formation is the use of cytotoxic organic solvents as the continuous phase in droplet generation processes. All-aqueous methods do not contain cytotoxic organic solvents but have so far been unable to achieve complete hydrogel gelation on chip. Here, we describe an enhanced droplet microfluidic platform that achieves on-chip gelation of all-aqueous hydrogel multicellular spheroids (MCSs). Specifically, we generate dextran-alginate droplets containing MCF-7 breast cancer cells, surrounded by polyethylene glycol, at a flow-focusing junction. Droplets then travel to a second flow-focusing junction where they interact with calcium chloride and gel on chip to form hydrogel MCSs. On-chip gelation of the MCSs is possible here because of an embedded capillary at the second junction that delays the droplet gelation, which prevents channel clogging problems that would otherwise exist. In drug-free experiments, we demonstrate that MCSs remain viable for 6 days. We also confirm the applicability of this system for cancer drug testing by observing that dose-dependent cell death is achievable using doxorubicin.

Pancreatic Cystic Lesions on MRI: What Is The Likelihood of a Present or Future Diagnosis of Pancreatic Carcinoma?

BACKGROUND: Pancreatic cystic lesions (PCLs) are followed for years due to older and likely biased works demonstrating a strong association with pancreatic carcinoma; more recent data are needed clarifying this relationship. PURPOSE: To determine the association between PCLs on MRI and a synchronous or future diagnosis of pancreatic carcinoma. STUDY TYPE: Single-center retrospective cohort. POPULATION: A total of 192 patients (111 female, 58%) with median age 66 years (range 26-87 years) with PCLs on abdominal MRI from 2011 to 2016. FIELD STRENGTH/SEQUENCES: 1.5 T and 3 T, including T2 WI, T1 WI, diffusion weighted imaging and contrast-enhanced T1 WI. ASSESSMENT: Each PCL was reviewed independently by 2 of 10 fellowship-trained abdominal radiologists. Fukuoka guideline worrisome features and high-risk stigmata were evaluated. Follow-up imaging and clinical notes were reviewed within a system that captures pancreatic carcinoma for the region, for a median follow-up of 67 months (interquartile range: 43-88 months). STATISTICAL TESTS: Pancreatic carcinoma prevalence and incidence rate for future carcinoma with 95% confidence intervals (95% CI). Fisher exact test, logistic regression with odds ratios (OR) and the Wilcoxon rank-sum test were used to assess PCL morphologic features with the Kolmogorov-Smirnov test used to assess for normality. P < 0.05 defined statistical significance. RESULTS: The prevalence of pancreatic carcinoma on initial MRI showing a PCL was 2.4% (95% CI: 0.9%, 5.2%). Thickened/enhancing cyst wall was associated with pancreatic carcinoma, OR 52 (95% CI: 4.5, 1203). Of 189 patients with a PCL but without pancreatic carcinoma at the time of initial MRI, one developed high-grade dysplasia and none developed invasive carcinoma for an incidence rate of 0.97 (95% CI: 0.02, 5.43) and 0 (95% CI: 0, 3.59) cases per 1000 person-years, respectively. DATA CONCLUSION: A low percentage of patients with a PCL on MRI had a pancreatic carcinoma at the time of initial evaluation and none developed carcinoma over a median 67 months of follow-up. EVIDENCE LEVEL: 3 TECHNICAL EFFICACY: 5.

Plug and Pop: A 3D-Printed, Modular Platform for Drug Delivery Using Clinical Ultrasound and Microbubbles.

Targeted drug and gene delivery using ultrasound and microbubbles (USMB) has the potential to treat several diseases. In vitro investigation of USMB-mediated delivery is of prime importance prior to in vivo studies because it is cost-efficient and allows for the rapid optimization of experimental parameters. Most in vitro USMB studies are carried out with non-clinical, research-grade ultrasound systems, which are not approved for clinical use and are difficult to replicate by other labs. A standardized, low-cost, and easy-to-use in vitro experimental setup using a clinical ultrasound system would facilitate the eventual translation of the technology to the bedside. In this paper, we report a modular 3D-printed experimental setup using a clinical ultrasound transducer that can be used to study USMB-mediated drug delivery. We demonstrate its utility for optimizing various cargo delivery parameters in the HEK293 cell line, as well as for the CMT167 lung carcinoma cell line, using dextran as a model drug. We found that the proportion of dextran-positive cells increases with increasing mechanical index and ultrasound treatment time and decreases with increasing pulse interval (PI). We also observed that dextran delivery is most efficient for a narrow range of microbubble concentrations.

Water-in-water droplet microfluidics: A design manual.

Droplet microfluidics is utilized in a wide range of applications in biomedicine and biology. Applications include rapid biochemical analysis, materials generation, biochemical assays, and point-of-care medicine. The integration of aqueous two-phase systems (ATPSs) into droplet microfluidic platforms has potential utility in oil-free biological and biomedical applications, namely, reducing cytotoxicity and preserving the native form and function of costly biomolecular reagents. In this review, we present a design manual for the chemist, biologist, and engineer to design experiments in the context of their biological applications using all-in-water droplet microfluidic systems. We describe the studies achievable using these systems and the corresponding fabrication and stabilization methods. With this information, readers may apply the fundamental principles and recent advancements in ATPS droplet microfluidics to their research. Finally, we propose a development roadmap of opportunities to utilize ATPS droplet microfluidics in applications that remain underexplored.

Controlled Shrinkage of Microfluidically Generated Microbubbles by Tuning Lipid Concentration.

Monodisperse microbubbles with diameters less than 10 µm are desirable in several ultrasound imaging and therapeutic delivery applications. However, conventional approaches to synthesize microbubbles, which are usually agitation-based, produce polydisperse bubbles that are less desirable because of their heterogeneous response when exposed to an ultrasound field. Microfluidics technology has the unique advantage of generating size-controlled monodisperse microbubbles, and it is now well established that the diameter of microfluidically made microbubbles can be tuned by varying the liquid flow rate, gas pressure, and dimensions of the microfluidic channel. It is also observed that once the microbubbles form, the bubbles shrink and eventually stabilize to a quasi-equilibrium diameter, and that the rate of stabilization is related to the lipid solution. However, how the lipid solution concentration affects the degree of bubble shrinkage, and the stable size of microbubbles, has not been thoroughly examined. Here, we investigate whether and how the lipid concentration affects the degree of microbubble shrinkage. Namely, we utilize a flow-focusing microfluidic geometry to generate monodisperse bubbles, and observe the effect of gas composition (2.5, 1.42, and 0.17 wt % octafluoropropane in nitrogen) and lipid concentration (1-16 mg/mL) on the degree of microbubble shrinkage. For the lipid system and gas utilized in these experiments, we observe a monotonic increase in the degree of microbubble shrinkage with decreasing lipid concentration, and no dependency on the gas composition. We hypothesize that the degree of shrinkage is related to lipid concentration by the self-assembly of lipids on the gas-liquid interface during bubble generation and subsequent lipid packing on the interface during shrinkage, which is arrested when a maximum packing density is achieved. We anticipate that this approach for creating and tuning the size of monodisperse microbubbles will find utility in biomedical applications, such as contrast-enhanced ultrasound imaging and ultrasound-triggered gene delivery.

Phase transition modulation and biophysical characterization of biomolecular condensates using microfluidics.

Membraneless organelles (MLOs) formed through liquid-liquid phase separation (LLPS) are becoming increasingly relevant to understanding viral-host interactions, neurodegenerative disease, and cancer. The modulation of LLPS involves many parameters and components. To describe these modulators, typical in vitro studies require laborious, manual sample preparation of different concentrations and costly biological reagents. Here, we introduce a minimal reagent, microfluidic platform to systematically generate samples of different concentrations and trigger phase separation. We demonstrate the platform's utility by constructing phase diagrams describing the modulation of LLPS using an aqueous two-phase system (ATPS) and an MLO-based phase separating system. We also show on-chip biophysical characterization typical of in vitro studies. We expect that this platform will be utilized by scientists to study the growing number of MLOs and inform clinical treatments for pathology related to LLPS.

Materials and methods for droplet microfluidic device fabrication.

Since the first reports two decades ago, droplet-based systems have emerged as a compelling tool for microbiological and (bio)chemical science, with droplet flow providing multiple advantages over standard single-phase microfluidics such as removal of Taylor dispersion, enhanced mixing, isolation of droplet contents from surfaces, and the ability to contain and address individual cells or biomolecules. Typically, a droplet microfluidic device is designed to produce droplets with well-defined sizes and compositions that flow through the device without interacting with channel walls. Successful droplet flow is fundamentally dependent on the microfluidic device - not only its geometry but moreover how the channel surfaces interact with the fluids. Here we summarise the materials and fabrication techniques required to make microfluidic devices that deliver controlled uniform droplet flow, looking not just at physical fabrication methods, but moreover how to select and modify surfaces to yield the required surface/fluid interactions. We describe the various materials, surface modification techniques, and channel geometry approaches that can be used, and give examples of the decision process when determining which material or method to use by describing the design process for five different devices with applications ranging from field-deployable chemical analysers to water-in-water droplet creation. Finally we consider how droplet microfluidic device fabrication is changing and will change in the future, and what challenges remain to be addressed in the field.

Identification and Adjudication of Adverse Events Following Rectal Cancer Surgery: Observational Case Series in a Region of Ontario, Canada.

BACKGROUND: For patients undergoing rectal cancer surgery, we evaluated whether suboptimal preoperative surgeon evaluation of resection margins is a latent condition factor-a factor that is common, unrecognized, and may increase the risk of certain adverse events, including local tumour recurrence, positive surgical margin, nontherapeutic surgery, and in-hospital mortality. METHODS: In this observational case series of patients who underwent rectal cancer surgery during 2016 in Local Health Integrated Network 4 region of Ontario (population 1.4 million), chart review and a trigger tool were used to identify patients who experienced the adverse events. An expert panel adjudicated whether each event was preventable or nonpreventable and identified potential contributing factors to adverse events. RESULTS: Among 173 patients, 25 (14.5%) had an adverse event and 13 cases (7.5%) were adjudicated as preventable. Rate of surgeon awareness of preoperative margin status was low at 50% and similar among cases with and without an adverse event (p = 0.29). Suboptimal surgeon preoperative evaluation of surgical margins was adjudicated a contributing factor in all 11 preventable local recurrence, positive margin, and nontherapeutic surgery cases. Failure to rescue was judged a contributing factor in the two cases with preventable in-hospital mortality. CONCLUSIONS: Suboptimal surgeon preoperative evaluation of surgical margins in rectal cancer is likely a latent condition factor. Optimizing margin evaluation may be an efficient quality improvement target.

Ultrasound and Microbubbles for Targeted Drug Delivery to the Lung Endothelium in ARDS: Cellular Mechanisms and Therapeutic Opportunities.

Acute respiratory distress syndrome (ARDS) is characterized by increased permeability of the alveolar-capillary membrane, a thin barrier composed of adjacent monolayers of alveolar epithelial and lung microvascular endothelial cells. This results in pulmonary edema and severe hypoxemia and is a common cause of death after both viral (e.g., SARS-CoV-2) and bacterial pneumonia. The involvement of the lung in ARDS is notoriously heterogeneous, with consolidated and edematous lung abutting aerated, less injured regions. This makes treatment difficult, as most therapeutic approaches preferentially affect the normal lung regions or are distributed indiscriminately to other organs. In this review, we describe the use of thoracic ultrasound and microbubbles (USMB) to deliver therapeutic cargo (drugs, genes) preferentially to severely injured areas of the lung and in particular to the lung endothelium. While USMB has been explored in other organs, it has been under-appreciated in the treatment of lung injury since ultrasound energy is scattered by air. However, this limitation can be harnessed to direct therapy specifically to severely injured lungs. We explore the cellular mechanisms governing USMB and describe various permutations of cargo administration. Lastly, we discuss both the challenges and potential opportunities presented by USMB in the lung as a tool for both therapy and research.

Microfluidic Generation of Monodisperse Nanobubbles by Selective Gas Dissolution.

Nanotechnology currently enables the fabrication of uniform solid nanoparticles and liquid nano-emulsions, but not uniform gaseous nanobubbles (NBs). In this article, for the first time, a method based on microfluidics that directly produces monodisperse NBs is reported. Specifically, a two-component gas mixture of water-soluble nitrogen and water-insoluble octafluoropropane as the gas phase are used in a microfluidic bubble generator. First, monodisperse microbubbles (MBs) with a classical microfluidic flow-focusing junction is generated, then the MBs shrink down to ≈100 nm diameter, due to the dissolution of the water-soluble components in the gas mixture. The degree of shrinkage is controlled by tuning the ratio of water-soluble to water-insoluble gas components. This technique maintains the monodispersity of the NBs, and enables precise control of the final NB size. It is found that the monodisperse NBs show better homogeneity than polydisperse NBs in in vitro ultrasound imaging experiments. Proof-of-concept in vivo kidney imaging is performed in live mice, demonstrating enhanced contrast using the monodisperse NBs. The NB monodispersity and imaging results make microfluidically generated NBs promising candidates as ultrasound contrast and molecular imaging agents.

Dosage-controlled intracellular delivery mediated by acoustofluidics for lab on a chip applications.

Biological research and many cell-based therapies rely on the successful delivery of cargo materials into cells. Intracellular delivery in an in vitro setting refers to a variety of physical and biochemical techniques developed for conducting rapid and efficient transport of materials across the plasma membrane. Generally, the techniques that are time-efficient (e.g., electroporation) suffer from heterogeneity and low cellular viability, and those that are precise (e.g., microinjection) suffer from low-throughput and are labor-intensive. Here, we present a novel in vitro microfluidic strategy for intracellular delivery, which is based on the acoustic excitation of adherent cells. Strong mechanical oscillations, mediated by Lamb waves, inside a microfluidic channel facilitate the cellular uptake of different size (e.g., 3-500 kDa, plasmid encoding EGFP) cargo materials through endocytic pathways. We demonstrate successful delivery of 500 kDa dextran to various adherent cell lines with unprecedented efficiency in the range of 65-85% above control. We also show that actuation voltage and treatment duration can be tuned to control the dosage of delivered substances. High viability (≥91%), versatility across different cargo materials and various adherent cell lines, scalability to hundreds of thousands of cells per treatment, portability, and ease-of-operation are among the unique features of this acoustofluidic strategy. Potential applications include targeting through endocytosis-dependant pathways in cellular disorders, such as lysosomal storage diseases, which other physical methods are unable to address. This novel acoustofluidic method achieves rapid, uniform, and scalable delivery of material into cells, and may find utility in lab-on-a-chip applications.

MRI LI-RADS Version 2018: Impact of and Reduction in Ancillary Features.

OBJECTIVE. The purpose of this study is to determine the impact of LI-RADS ancillary features on MRI and to ascertain whether the number of ancillary features can be reduced without compromising LI-RADS accuracy. MATERIALS AND METHODS. A total of 222 liver observations in 81 consecutive patients were identified on MRI between August 2013 and December 2018. The presence or absence of major and ancillary features was used to determine the LI-RADS category for LR-1 to LR-5 observations. Final diagnosis was established on the basis of pathologic findings or one of several composite clinical reference standards. Diagnostic accuracy was compared with and without ancillary features by use of the z test of proportions. Decision tree analysis and machine learning-based feature pruning were used to identify noncontributory ancillary features for LI-RADS categorization. Interobserver agreement with and without ancillary features was measured using the Krippendorff alpha coefficient, and comparisons were made using bootstrapping. A p < .05 was considered statistically significant. RESULTS. Application of ancillary features resulted in a change in the LI-RADS category of seven hepatocellular carcinomas (HCCs), with the category of six of seven (86%) HCCs upgraded; 51 benign observations also had a change in LI-RADS category, with the category of 33 (65%) of these observations downgraded. When ancillary features were applied, the percentage of HCCs in each LI-RADS category did not differ significantly compared with major features alone (p = .06-.49). Decision tree analysis and the machine learning model identified five ancillary features as noncontributory: corona enhancement, nodule-in-nodule, mosaic architecture, blood products in mass, and fat in a mass, more than in adjacent liver. Interobserver agreement was high with and without application of ancillary features; however, it was significantly higher without ancillary features (p < .001). CONCLUSION. Although ancillary features are an important component of LI-RADS, their impact may be small. Several ancillary features likely can be removed from LI-RADS without compromising diagnostic performance.

An ultrafast enzyme-free acoustic technique for detaching adhered cells in microchannels.

Adherent cultured cells are widely used biological tools for a variety of biochemical and biotechnology applications, including drug screening and gene expression analysis. One critical step in culturing adherent cells is the dissociation of cell monolayers into single-cell suspensions. Different enzymatic and non-enzymatic methods have been proposed for this purpose. Trypsinization, the most common enzymatic method for dislodging adhered cells, can be detrimental to cells, as it can damage cell membranes and ultimately cause cell death. Additionally, all available techniques require a prolonged treatment duration, typically on the order of minutes (5-10 min). Dissociation of cells becomes even more challenging in microfluidic devices, where, due to the nature of low Reynolds number flow and reduced mixing efficiency, multiple washing steps and prolonged trypsinization may be necessary to treat all cells. Here, we report a novel acoustofluidic method for the detachment of cells adhered onto a microchannel surface without exposing the cells to any enzymatic or non-enzymatic chemicals. This method enables a rapid (i.e., on the order of seconds), cost-effective, and easy-to-operate cell detachment strategy, yielding a detachment efficiency of ∼99% and cellular viability similar to that of the conventional trypsinization method. Also, as opposed to biochemical-based techniques (e.g., enzymatic), in our approach, cells are exposed to the dissociating agent (i.e., substrate-mediated acoustic excitation and microstreaming flow) only for as long as they remain attached to the substrate. After dissociation, the effect of acoustic excitation is reduced to microstreaming flow, therefore, minimizing unwanted effects of the dissociating agent on the cell phenotype. Additionally, our results suggest that cell excitation at acoustic powers lower than that required for complete cell detachment can potentially be employed for probing the adhesion strength of cell-substrate attachment. This novel approach can, therefore, be used for a wide range of lab-on-a-chip applications.

Biomedical nanobubbles and opportunities for microfluidics.

The use of bulk nanobubbles in biomedicine is increasing in recent years, which is attributable to the array of therapeutic and diagnostic tools promised by developing bulk nanobubble technologies. From cancer drug delivery and ultrasound contrast enhancement to malaria detection and the diagnosis of acute donor tissue rejection, the potential applications of bulk nanobubbles are broad and diverse. Developing these technologies to the point of clinical use may significantly impact the quality of patient care. This review compiles and summarizes a representative collection of the current applications, fabrication techniques, and characterization methods of bulk nanobubbles in biomedicine. Current state-of-the-art generation methods are not designed to create nanobubbles of high concentration and low polydispersity, both characteristics of which are important for several bulk nanobubble applications. To date, microfluidics has not been widely considered as a tool for generating nanobubbles, even though the small-scale precision and real-time control offered by microfluidics may overcome the challenges mentioned above. We suggest possible uses of microfluidics for improving the quality of bulk nanobubble populations and propose ways of leveraging existing microfluidic technologies, such as organ-on-a-chip platforms, to expand the experimental toolbox of researchers working to develop biomedical nanobubbles.

Lab on a rod: Size-based particle separation and sorting in a helical channel.

Size-based particle separation using inertial microfluidics in spiral channels has been well studied over the past decade. Though these devices can effectively separate particles, they require a relatively large device footprint with a typical outer channel radius of approximately 15 mm. In this paper, we describe a microfluidic device with a footprint diameter of 5.5 mm, containing a helical channel capable of inertial particle separation fabricated using abrasive jet micromachining. The separation of particles in several channel geometries was studied using wide-field fluorescence microscopy. A maximum separation efficiency of approximately 90% was achieved at a flow rate of 1.5 ml/min with a purity of approximately 95% at the outlet, where large particles were collected. An accompanying computational fluid dynamics model was developed to allow researchers to quickly assess the separation capability of their helical or spiral devices.

Evaporation-Driven Water-in-Water Droplet Formation.

We present new observations of aqueous two-phase system (ATPS) thermodynamic and interfacial phenomena that occur inside sessile droplets due to water evaporation. Sessile droplets that contain polymeric solutions, which are initially in equilibrium in a single phase, are observed at their three-phase liquid-solid-air contact line. As evaporation of a sessile droplet proceeds, we find that submicron secondary water-in-water (W/W) droplets emerge spontaneously at the edges of the mother sessile droplet due to the resulting phase separation from water evaporation. To understand this phenomenon, we first study the secondary W/W droplet formation process on different substrate materials, namely, glass, polycarbonate (PC), thermoplastic elastomer (TPE), poly(dimethylsiloxane)-coated glass slide (PDMS substrate), and Teflon-coated glass slide (Teflon substrate), and show that secondary W/W droplet formation arises only in lower-contact-angle substrates near the three-phase contact line. Next, we characterize the size of the emergent secondary W/W droplets as a function of time. We observe that W/W drops are formed, coalesced, aligned, and trapped along the contact line of the mother droplet. We demonstrate that this W/W multiple emulsion system can be used to encapsulate magnetic particles and blood cells, and achieve size-based separation. Finally, we show the applicability of this system for protein sensing. This is the first experimental observation of evaporation-induced secondary W/W droplet generation in a sessile droplet. We anticipate that the phenomena described here may be applicable to some biological assay applications, for example, biomarker detection, protein sensing, and point-of-care diagnostic testing.